The hydraulic system of many machines have an oil processing circuit such as an oil cooler for cooling the oil being returned to a hydraulic tank. One of the problems encountered is that the oil becomes extremely viscous at extremely cold temperatures and some failures have occurred in the cooler due to high oil pressures generated by forcing the viscous oil through the cooler when a cold machine is started and then operated at normal speeds before the hydraulic system has warmed sufficiently. Another problem encountered is that an oil cooling fan associated with the oil cooler on some systems runs continuously and the oil cannot reach normal operating temperatures in cold ambient conditions.
In view of the above, it would be desirable to provide an oil cooler circuit in which oil flow through the cooler is prevented when the oil temperature is at or below a predetermined level.
The present invention is directed to overcoming one or more of the problems as set forth above.